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Calculating flow variables only once in begin_f_loop()

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Old   June 25, 2020, 03:14
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so I have written a code for " Tf = Ts + ks(dT/dn)" in which Tf is fluid temperature, Ts is the wall temperature and ks is temperature jump coefficient.

DEFINE_PROFILE(temperaturejump, thread, position)
{
face_t f;
cell_t c;
Thread *tc;
double b = 0.000001;
double dTdy ,tem ,walltemp;
begin_f_loop(f, thread)
{
c = F_C0(f,thread);
tc = THREAD_T0(thread);
dTdy = C_T_G(c,tc)[1];
walltemp = F_T(f, thread);
tem = (b*dTdy) + walltemp;
F_PROFILE(f, thread, position) = tem;
}
end_f_loop(f, thread)
}

is it correct or does it have any problem??
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Old   June 25, 2020, 03:19
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The code is correct, but missing the commands that I shared earlier for storing temperature gradient.
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Old   June 25, 2020, 03:37
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so should i add them within the loop?
and another question is that does the expression "F_T(f, thread)" gives wall temperature? or do i have to use "C_T(c, thread)" instead?
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Old   June 25, 2020, 03:43
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You need to add those three lines outside the loop.

F_T is good. C_T gives cell temperature.
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Old   June 25, 2020, 03:56
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okay. but im having a trouble with hooking the UDFs. where do i have to hook this temperature jump? for the face (adjacent to solid) or for the shadow(adjacent to fluid) ??
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Old   June 25, 2020, 05:57
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The profiles are same for a wall and its shadow. If you hook it to one, it automatically works for the other. And that's where you have trouble since the jump should exist only on the fluid side. So, DEFINE_PROFILE may not be a good idea. Use DEFINE_ADJUST, access the thread on the fluid size, and then change the temperature. Let the coupled condition be as it is so that thermal energy conservation could be maintained.
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Old   June 25, 2020, 08:23
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aha I think I understand what you are saying, do you mean if I use DEFINE_ADJUST, it would implement the heat transfer(conduction) between the face and its shadow by itself too, right?
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Old   June 25, 2020, 09:06
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That's what a default coupled condition does. In reality, there is no conduction between a boundary and its shadow. They are same. When they are coupled, the heat flux entering one is equal to heat flux exiting other, i.e., thermal energy is conserved.
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Old   June 25, 2020, 09:22
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but the problem Im having here is that I need to apply both conditions to the liquid-solid interface, I mean I need to apply temperature jump to shadow(adjacent to fluid) temperature and also I need to have a coupled condition between face and shadow. but in fluent I can only either apply temperature jump or just have coupled condition, not both of them at a time. what should I do?
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Old   June 25, 2020, 10:00
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That's why you need to use DEFINE_ADJUST. You can apply jump using UDF and coupled condition will maintain the conservation across shadow pairs.
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Old   June 25, 2020, 10:27
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okay. now I understand. thank you very much for your help
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Old   June 25, 2020, 11:22
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so I have read about DEFINE_ADJUST macro. but I dont know how does it work!? what are the differences between this and DEFINE_PROFILE? which arguments should I use ? and to which part of FLUENT should I apply that?
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Old   June 27, 2020, 09:31
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You mean first I have to write a DEFINE_ADJUST which includes temperature jump function in it and hook it to function hooks and then leave the thermal boundary conditions for faces and their shadows as coupled. right?
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Old   June 30, 2020, 10:55
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Hi again
I have written a code by DEFINE_ADJUST for temperature jump as follows :

DEFINE_ADJUST(temperaturejump3, domain)
{
Domain *d;
int zone_ID = 16;
Thread *f_thread = Lookup_Thread(domain, zone_ID);
Thread *c_thread;
cell_t cell;
face_t face;
double dTdy, temp, walltemp;
double b = 0.000001;
thread_loop_f (f_thread,domain)
{
begin_f_loop(face,f_thread)
{
cell = F_C0(face,f_thread);
c_thread = THREAD_T0(f_thread);
walltemp = F_T(face,f_thread);
dTdy = C_T_G(cell,c_thread)[1];
F_PROFILE(face, f_thread, zone_ID) = (b*dTdy) + walltemp;
}
end_f_loop(face,f_thread)
}
}

is it correct or does it need any modifying??

Thanks in advance
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